The present invention relates to a method of creating a fluid meter housing. More specifically, the present invention provides a method of manufacturing the housing for a fluid meter in which a molten material is injected into a cavity formed between a core and a mold. The core and mold are configured so that the cavity is shaped as desired for the fluid meter housing. After allowing the molten material to harden, the housing and enclosed core are removed from the mold. The core is then heated to its melting point and drained from within the fluid meter housing.
Fluid meters have traditionally been constructed from various metals such as bronze and copper. As new materials and methods of using them have developed, the economic feasibility of substituting such materials for metals in the construction of fluid meters has improved. Thermoplastics represent one such class of material that can not only result in savings in the cost of materials but can also be more suitable for use with certain fluids.
Traditionally, plastic parts have been molded using conventional plastic injection molding techniques. Such techniques generally involve creating a mold having an internal cavity into which the plastic is injected in a molten state. Upon cooling the mold, the resulting plastic part may be removed by extraction or by opening the mold. Such techniques have been streamlined for mass production of plastic parts ranging from computer connectors to automobile components.
Unfortunately, traditional plastic injection molding techniques are difficult to apply when the part being manufactured has complex internal configurations. Fluid meters generally have complex internal passage ways complicating the use of conventional plastic injection molding techniques to manufacture housings or casings for fluid meters. While it is possible to manufacture such housings using conventional molding techniques, this proves to be time consuming and labor intensive.
For example, FIG. 1 depicts a cross-section of an exemplary mold 20 used with conventional plastic injection molding techniques. Mold 20 includes a cavity defined in part by internal walls 22 which correspond in shape to the external surface of a desired fluid meter housing. Multiple interconnected inserts 24, shown in FIG. 2, are placed within the cavity and correspond in shape to the internal surface of the fluid meter housing 26. Interconnected inserts 24 are typically constructed from a metal, such as stainless steel, having a relatively high melting point. Using the specifications of the fluid meter housing 26 sought to be formed, interconnected inserts 24 are carefully machined so that when assembled the external surface of the interconnected inserts 24 conforms to the internal surface of the fluid meter housing 26. Together, inserts 24 and internal walls 22 configure the shape of the cavity to correspond to the shape of housing 26.
Upon placing interconnecting inserts 24 into the cavity, mold 20 is closed under a press capable of applying forces of up to 150 tons to maintain closure of the mold 20. While closed, a molten thermoplastic material is injected at high pressures through port 28. A sufficient amount of material must be injected to fill the cavity that exists between walls 22 of mold 20 and the external surface of interconnected inserts 24. As the molten thermoplastic material begins to cool, it also begins to solidify and assume the shape of the fluid meter housing 26. Simultaneously, the thermoplastic material also begins to shrink. As a result, mold 20 must be quickly reopened so that fluid meter housing 26, now containing interconnecting inserts 24, can be removed. Interconnecting inserts 24 are then removed from the interior of housing 26. If the removal of interconnecting inserts 24 is not performed quickly after the thermoplastic material begins to cool, the interconnecting inserts 24 will be trapped inside the fluid meter housing 26.
The conventional technique above described is disfavored for several reasons. First, the temperature required for injecting the molten thermoplastic material complicates the handling of interconnecting inserts 24. Gloves or special equipment must be used to maneuver the inserts 24. Second, interconnecting inserts 24 are expensive to manufacture and a set is required for each mold being used in the manufacturing process. Third, if the interconnecting inserts 24 are not rapidly removed as the thermoplastic material cools, fluid meter housing 26 must be destroyed in order to remove the interconnecting inserts 24, and the entire process must be repeated.
The present invention provides a method of manufacturing a housing or casing for a fluid meter. In one example, the method of the present invention provides for injecting a molten material into a cavity or space formed between a core and a mold. The core and mold are configured such that the cavity between the surfaces of the core and mold forms the shape of the desired fluid meter housing. Upon allowing the molten material to cool or become rigid, the housing and the enclosed core are removed from the mold. The core is then heated to its melting point, or otherwise liquified, and drained or removed from inside the fluid meter housing. The present invention overcomes disadvantages of the prior art by providing a process whereby a fluid meter housing having relatively complex internal characteristics may be manufactured without the necessity of using expensive inserts or having to rapidly disassemble such inserts at high temperatures.
While variations of the present invention may be envisioned using the teachings disclosed herein, in one example of the present invention a first mold is provided having an internal surface that corresponds to the desired internal shape for a fluid meter housing. A metal in a molten state is injected into this first mold. The molten metal is then cooled until the metal solidifies to form a metal core in the shape of the internal surface of the fluid meter housing. After cooling, the resulting metal core is removed from the first mold.
A second mold is a provided having an internal surface that corresponds to the external shape desired for the fluid meter housing. This second mold and the core are configured so that upon placing the core into the second mold, a cavity is created that corresponds to the shape of the desired fluid meter housing. Upon placing the metal core into the second mold so as to create this cavity, a molten thermoplastic material is injected into the cavity so as to fill the cavity and form the fluid meter housing between the metal core and the second mold. The second mold and thermoplastic material are then cooled to cause the thermoplastic material to solidify into the shape of the fluid meter housing. The resulting fluid meter housing is then removed from the second mold. At this point in the process, the fluid meter housing may still contain the metal core. The metal core is heated until the metal reaches a molten state and can then be removed from the fluid meter housing. Alternatively, the metal core may be removed while the fluid meter housing is still within the second mold. This alternative requires that the materials used to construct the molds and housing have appropriate relative melting point temperatures.
The first and second mold can be configured with a variety of features desired for the fluid meter housing. By way of example only, the first and second molds may be configured for defining a fluid inlet and a fluid outlet for the housing. The first and second molds may also be configured for providing a plurality of tabs and a locking boss on the surface of the housing such that a register or other device may be attached. The first and second molds may also be configured such that the fluid meter housing is provided with resealable threaded connectors at the fluid inlet and the fluid outlet for connecting the housing to conduit or to the path of flow.
In another exemplary process of the present invention, a metal is heated until reaching a molten state. A first die is provided having an internal surface that is shaped identically to the internal surface of a desired fluid meter housing. The molten metal is inserted into the first die and then the temperature of the molten metal is lowered until the metal becomes capable of sustaining shape. This shape will correspond to the internal surface of the first die and therefore the internal surface of the fluid meter housing. The resulting metal shape is removed from the first die.
A second die is provided having an internal surface shaped to form the external surface of the fluid meter housing being manufactured. This second die is also configured for forming a cavity between the internal surface of the second die and the metal shape that corresponds to the geometry and thickness of the fluid meter housing. The cavity is created upon placing the metal shape into the second die. Molten plastic is then inserted into the cavity between the metal shape and the second die. After insertion, the molten plastic is cooled until it becomes rigid enough to retain the shape of the cavity and thereby form the fluid meter housing. The metal shape and housing are removed from the second die. The temperature of the metal shape is then raised until the metal becomes molten, thereby allowing the metal to be removed from the interior of the fluid meter housing.
In still another example of the present invention, a first material is provided having a melting temperature of T1. Using this first material, a core is formed having the desired geometry to form the internal shape of a fluid meter casing. Similarly, a shell is provided having an internal surface that corresponds to the external shape of the fluid meter casing. The core is located inside the shell so as to provide a space between the core and the shell that corresponds to the shape and dimensions of the fluid meter casing.
A second material is also provided having a melting temperature of T2. Melting temperature T2 of the second material must be greater than the melting temperature T1 of the first material. The second material is injected in a molten state into the space formed between the core and the shell. The second material is allowed to cool to a temperature less than T2 so that the second material will solidify and form into the shape of the fluid meter casing. Upon cooling, the fluid meter casing now contains the first material and may be removed from the shell. The first material is then heated to a temperature greater than T1 but less than T2. As a consequence, the first material will melt without melting the second material that forms the fluid meter casing. The first material may thereby be removed from the interior of the fluid meter casing.
In another example of the present invention, a meltable insert is positioned within a mold. The insert and the mold are both configured so as to create a void between the adjacent surfaces of the insert and the mold that is equivalent in shape and thickness to a fluid meter housing. A material is then introduced in a fluid state into the void so as to substantially fill the void. The temperature of the material is then reduced until the material becomes sufficiently rigid to maintain the shape of the fluid meter housing formed by the void. The fluid meter housing may then be removed from the mold. At this point in process, the fluid meter housing may still contain the insert. The insert is then heated until a temperature is reached at which the insert flows out of the fluid meter housing. This step may also be formed while the fluid meter is still within the mold if appropriate materials are selected for creating the insert, mold, and fluid meter housing.
In still another example of the present invention, a module is provided that corresponds to the internal shape of a casing for fluid meter. This module is constructed from a material that is meltable. A chamber is provided having an internal surface that corresponds to the external surface of the casing. The module is placed into the chamber so as to create a volume that corresponds to the shape and thickness of the casing. The resulting volume is then filled with a liquid. The liquid is then caused to harden and thereby assume the shape of the volume and form the desired casing. The module is then melted so as to enable the module to be removed from the casing. The casing may then be removed from the chamber. Alternatively, the casing may be removed from the chamber while still containing the module; and then the module may be melted so as to enable it to be removed from the casing.
Although the present invention has been discussed in terms of using a thermoplastic material for the construction of the meter housing, the present invention is not limited to such thermoplastic materials. Any material capable of being injected into the cavity and having a melting point higher than the melting point of the material used for the core may be utilized. Similarly, the core may be constructed from any material that will not chemically or physically react with the material selected for the fluid meter housing and is not limited to a metal alloy. However, the core must be constructed from a material having a melting point lower than the melting point of the material selected for the fluid meter housing if heat or elevated temperature is used to remove the core from the housing.
Additional objects and advantages of the invention are set forth in, or will be apparent to, those of ordinary skill in the art from the detailed description as follows. Also, it should be further appreciated that modifications and variations to the specifically illustrated and discussed features and variations hereof may be practiced in various embodiments and uses of this invention without departing from the spirit and scope thereof by using the teachings disclosed herein. Such variations may include, but are not limited to, substitutions of equivalent means, steps, features, and materials for those shown and discussed, and the functional or positional reversal or change in sequence of various means, steps, features, or the like.